Research Of Satellite Altimetry Waveforms Retracking Algorithms And Application Over Yellow Sea And Bohai Sea

The measurement accuracy of satellite altimetry is 5 cm on the ocean. But in coastal waters, the altimeter waveforms are out of shape affected by coastal land, ocean topography and geophysical environment.The quality of altimetry data decline severely, leading to the lack of altimetry data.Coastal waters affect the human activity very much, and it is important to having a clear understanding.So it is necessary to retrack coastal altimetry data to improve the quality of coastal altimetry data.In this paper, the Jason-1 SGDR waveform data over Yellow Sea and Bohai Sea was precessed using waveform retracking algorithms. Based on the retracked Jason-1 data, this paper compared the sea surface height with MSS_CNES_CLS11 model, and researched the suitable algorithm for Jason-1 waveforms over Yellow Sea and Bohai Sea. The achievements are got as follows:(1)Analysis of the altimetry waveforms over Yellow Sea and Bohai Sea. Affected by land signal, the waveforms distort at the junction of land and ocean and the region of many islands. The altimeter has lost lock on the leading edge on land/ocean transition, leading to data missing.(2)Over Yellow Sea and Bohai Sea, 96.31 percent of the leading edge midpoints computed by the threshold algorithm are between 30 and 32. The percentage of contaminated waveforms is about 3.69%.(3)The improved β-5 algorithm has stronger fitting ability and less data loss than the β-5 algorithm. We got 3365 more valid 20 Hz data points each cycle with the improved β-5 algorithm than the β-5 algorithm. Comparing the sea surface height retacked by improved β-5 algorithm with the one retracked by satellite algorithm, the RMS is 0.12 m, smaller than the β-5 algorithm.(4)The RMS of the difference between the sea surface height retracked by multi-leading edge and multi-threshold algorithm and the one retracked by satellite algorithm is 0.09 m, better than the improved β-5 algorithm.(5)Comparing the sea surface height retracked by the improved β-5 algorithm with MSS_CNES_CLS11 model along orbit, the mean difference is 0.103 m, and the RMS is 0.148 m, smaller than the satellite retracking sea surface height. The mean difference between the multi-leading edge and multi-threshold algorithm and MSS_CNES_CLS11 model is 0.092 m, and the RMS is 0.144 m, smaller than both the satellite retracking algorithm and the improved β-5 algorithm. The multi-leading edge and multi-threshold algorithm is more suitable for Yellow Sea and Bohai Sea than the improved β-5 algorithm.